Method and system for using enhanced primary synchronization signal for resynchronization

ABSTRACT

A method and apparatus for using enhanced PSS (ePSS) transmitted from a base station, for example an eNB, for use by UEs for resynchronization of the UE with the base station is disclosed. According to some embodiments, when resynchronization using the ePSS fails on the first attempt, the UE non-coherently or coherently combines the ePSS with the legacy PSS/SSS in order to resynchronize the UE with the base station. According to some embodiments, when resynchronization using the ePSS fails on the first attempt, the UE non-coherently or coherently combines the ePSS reception results with the legacy PSS/SSS reception results in order to resynchronize the UE with the base station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/500,324 entitled “Method and System for UsingEnhanced Primary Synchronization Signal for Resynchronization” filed May2, 2017, the contents of which are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The present invention pertains in general to the field of wirelesscommunications systems such as the Long Term Evolution (LTE) system andin particular to a method and system for using an enhanced PrimarySynchronization Signal for resynchronization.

BACKGROUND

Coverage of mobile User Equipment (UE) in 3GPP′ LTE systems is anongoing concern. The desire is to provide connectivity to UEs inmarginal signal strength conditions without excessive power consumptionrequirements placed on the UE.

One task required by a UE when it wishes to camp on an LTE cell is toperform cell synchronization. Synchronization includes detecting thePrimary Synchronization Signal (PSS) and the Secondary SynchronizationSignal (SSS) transmitted by the cell's evolved NodeB (eNB) base station.The PSS is used to indicate the cell identity within a group of cells,and the SSS is used to indicate the cell identity group number. Threedifferent PSS signals and 168 different SSS signals are typicallyavailable. An eNB may use a particular combination of both identifiersto convey its cell-ID. A hierarchical cell search is performed by the UEto identify the cell-ID by analysis of the particular PSS and SSStransmitted by the cell's eNB.

However, standard methods of detecting the PSS and SSS can consumerelatively large amounts of time and energy, particularly in marginalsignal conditions and/or when Discontinuous Reception (DRX) is employedby a UE.

There is a requirement for LTE Cat-M1 (LTE-M) and narrow bandInternet-of-things (NB-IOT) to support a high maximum coupling loss(MCL), for example 164 dB. However, for resynchronization, for exampleresynchronization after a UE comes out of a deep sleep from power savingmode (PSM) or discontinuous reception (DRX) or extended DRX, where thecell providing service to the UE has not changed but the carrierfrequency offset (CFO) and timing are unknown, it is difficult toachieve a similar high MCL and achieving the high MCL can take a longtime using significant UE power and increased latency. FIG. 1illustrates the performance of legacy PSS/SSS for resynchronization,under the assumption that the UE knows the SSS and PSS sequences. As canbe seen in FIG. 1, the legacy PSS/SSS 90^(th) percentileresynchronization can take approximately 2.5 seconds at 164 dB MCL. Assuch, the time period for resynchronization can be prohibitively long.

Therefore there is a need for a method and system for using enhancedPrimary Synchronization Signals for resynchronization that is notsubject to one or more limitations of the prior art.

This background information is provided to reveal information believedby the applicant to be of possible relevance to the present invention.No admission is necessarily intended, nor should be construed, that anyof the preceding information constitutes prior art against the presentinvention.

SUMMARY

An object of the present invention is to provide a method and system forusing enhanced Primary Synchronization Signals for resynchronization. Inaccordance with an aspect of the present invention, there is provided amethod for resynchronizing a User Equipment (UE) to a base station. Themethod includes receiving, by a UE, a first set of synchronizationsignals and a second set of synchronization signals. The method furtherincludes resynchronizing, by the UE, with the base station using thesecond set of synchronizing signals.

In accordance with another aspect of the present invention, there isprovided a User Equipment (UE) for resynchronization with a basestation. The UE includes a processor and a machine readable memorystoring machine executable instructions. The machine readableinstructions, when executed by the processor configure the userequipment to receive a first set of synchronization signals and a secondset of synchronization signals. The machine readable instructions, whenexecuted, further configure the UE to resynchronize with the basestation using the second set of synchronizing signals.

According to some embodiments, when resynchronizing with the basestation using the second set of synchronizing signals fails, the methodfurther includes combining, by the UE, the first set of synchronizingsignals and the second set of synchronizing signals to form a modifiedset of synchronizing signals and resynchronizing, by the UE, with thebase station using the modified set of synchronizing signals. Accordingto some embodiments, the combining is non-coherent combining. In someembodiments, the combining is coherent combining.

According to some embodiments, the second set of synchronization signalsare time adjusted before combining the first set of synchronizingsignals and the second set of synchronizing signals. In someembodiments, the first set of synchronization signals are time adjustedbefore combining the first set of synchronizing signals and the secondset of synchronizing signals. In some embodiments, the first set ofsynchronization signals are zero padded before combining the first setof synchronizing signals and the second set of synchronizing signals.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the performance of legacy PSS and SSS forresynchronization of a UE with an eNB, when the UE previously knows thePSS and SSS.

FIG. 2 illustrates a system including an evolved NodeB (eNB) and atleast one User Equipment (UE), provided and configured in accordancewith embodiments of the invention.

FIG. 3 illustrates a method for facilitating synchronization of a UE toa Long Term Evolution (LTE) cell serviced by an eNB, provided inaccordance with embodiments of the invention.

FIG. 4 illustrates portions of an LTE Resource Grid includingtransmission of a burst of multiple signals for use in UEsynchronization, in accordance with embodiments of the presentinvention.

FIG. 5 illustrates simulation results corresponding to detection of thePrimary Synchronization Signal (PSS), in accordance with embodiments ofthe present invention.

FIG. 6 illustrates portions of an LTE Resource Grid includingtransmission of a burst of multiple signals for use in UEsynchronization, in accordance with embodiments of the presentinvention.

FIG. 7 illustrates portions of an LTE Resource Grid includingtransmission of a burst of multiple signals for use in UEsynchronization, in accordance with other embodiments of the presentinvention.

FIG. 8 illustrates simulation results corresponding to detection of thePSS, in accordance with embodiments of the present invention and/or theprior art.

FIG. 9 illustrates an example of legacy and coverage-enhanced paging, inaccordance with embodiments of the present invention.

FIG. 10 illustrates a cell pattern of re-use of different roots ofZadoff-Chu sequences for the ePSS, in accordance with embodiments of thepresent invention.

FIG. 11 illustrates portions of an LTE Resource Grid includingtransmission of a burst of multiple signals for use in UEsynchronization, in accordance with other embodiments of the presentinvention.

FIG. 12 illustrates ePSS and PO timing with a 3.6 second interval, inaccordance with an embodiment of the present invention.

FIG. 13 illustrates ePSS with paging indicator, in accordance with anembodiment of the present invention.

FIG. 14 illustrates the performance of using ePSS for resynchronizationof a UE with a base station, in accordance with an embodiment of thepresent invention.

FIG. 15 illustrates the placement of ePSS in relation to PSS/SSS forresynchronization of a UE with a base station, in accordance withembodiments of the present invention.

FIG. 16 illustrates a base station, for example an eNB and a UE providedin accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

In current LTE implementations, the Primary Synchronization Signal (PSS)and the Secondary Synchronization Signal (SSS) are used forsynchronization of UEs in order to facilitate further communication viathe LTE network, as would be readily understood by a worker skilled inthe art.

In various existing LTE implementations, the PSS uses a Zadoff-Chusequence which is widely used in LTE, including use for the uplinkreference signals and random access preambles. Such sequences may bepreferred because of their Constant Amplitude Zero Autocorrelation(CAZAC) property. A mathematical representation of such Zadoff-Chusequences is as follows:ZC ⁶³ _(M)(n)=exp[−jπMn(n+1)/63],n=0,1, . . . ,62  (1)

In typical existing LTE implementations, only three of the possible 63roots are used by the PSS. These roots correspond to M=29, 34 and 25 inEquation (1). As such, it is recognized herein that 33 other roots arestill available for use because roots that may be used must be co-prime.

In various existing LTE implementations, such as Frequency DivisionDuplexing (FDD) implementations with normal cyclic prefix and 20 MHzsystem bandwidth, the PSS and SSS are transmitted via 6 contiguousPhysical Resource Blocks (PRBs) located at the center frequencies. Forexample when Resource Blocks 0 to 99 are implemented, the PRBs maycorrespond to Resource Blocks 47 to 52. The PSS may be transmitted inthe last PRBs of a subframe while the SSS may be transmitted in thenext-to-last PRBs of a subframe.

In various existing LTE implementations, the SSS depends on the group-IDand the sector-ID. To each possible group-ID, a pair of numbers m0 andml is assigned. Through those numbers, two sequences s0 and s1 can begenerated using a length 31 linear feedback shift register. Thosemaximum-length sequences are then interleaved in the frequency domain.Afterwards there is a scrambling applied on the even and the oddsubcarrier entries separately. For the scrambling, two additionalsequences c0 and c1 are generated that are both based on a basescrambling code C. The shift value between the sequences indicates thesector-ID Ns. Further information about the generation of the basescrambling can be found in the 3GPP specification document numbered 3GPPTS 36.201 and entitled “3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); LTE physical layer; General description (Release12),” Version 12.1.0 of which is dated December, 2014.

It is noted that the two transmissions of the SSS within a 10 ms Frameare different. Therefore a UE may detect which SSS transmission is thefirst in a frame and which SSS transmission is the second in a frame.

It is further noted that, for practical purposes, the SSS arem-sequences and thus exhibit relatively poor auto-correlation propertieswhen compared to the Zadoff-Chu sequences used for the PSS.

DRX and Paging

Discontinuous Reception (DRX) is intended to improve UE battery life byallowing the UE enter an Idle mode and refrain from decoding downlinkdata in certain time periods, as would be readily understood by a workerskilled in the art. During DRX, in Idle mode, a UE may save power whenit only monitors the Physical Downlink Control Channel (PDCCH) on onepre-determined Paging Occasion (PO) per DRX cycle, as specified forexample in the 3GPP specification document numbered 3GPP TS 36.304 andentitled “3rd Generation Partnership Project; Technical SpecificationGroup Radio Access Network; Evolved Universal Terrestrial Radio Access(E-UTRA); User Equipment (UE) procedures in idle mode (Release 12),”Version 12.3.0 of which is dated December 2014. The paging indicationfor the UE is received through Paging Radio Network Temporary Identifier(P-RNTI) on the PDCCH. If the UE does not find P-RNTI, it goes back tosleep. If the UE finds P-RNTI, it proceeds to decode Physical DownlinkShared Channel (PDSCH). The PDSCH will contain the SAE Temporary MobileSubscriber Identity (S-TMSI) or International Mobile Security Identity(IMSI) list of UEs being paged. If the UE finds its S-TMSI or IMSI ID inthe list, then it knows that it is paged. If not, it will go back tosleep.

ePSS

In accordance with embodiments of the present invention, there isprovided a method and apparatus for wirelessly transmitting an enhancedPSS (ePSS) from an eNB for use by UEs. The ePSS functions similarly tothe existing PSS but includes multiple copies of signals comparable tothe existing PSS. Each of these multiple copies may be referred toherein as a component signal of the ePSS. The component signals may betransmitted in a burst, i.e. within a relatively short time frame. Invarious embodiments, the ePSS may be transmitted via the LTE ResourceElements (REs) which are, in current LTE systems, normally reserved forthe Physical Downlink Shared Channel (PDSCH). UEs may be configured toreceive and use the multiple copies inherent in the ePSS to decreasedetection time and/or energy expenditure used for detection.

In accordance with embodiments of the present invention, there isprovided a method and apparatus for using enhanced PSS (ePSS)transmitted from a base station, for example an eNB, for use by UEs forresynchronization of the UE with the base station. According to someembodiments, when resynchronization using the ePSS fails on the firstattempt, the UE non-coherently or coherently combines the ePSS with thelegacy PSS/SSS in order to resynchronize the UE with the base station.According to some embodiments, when resynchronization using the ePSSfails on the first attempt, the UE non-coherently or coherently combinesthe ePSS reception results with the legacy PSS/SSS reception results inorder to resynchronize the UE with the base station.

It is understood that the ePSS can include repetitions of one or more ofPSS, SSS or other synchronization signals that can be used in a LTEcommunication network or other communication system, as would be readilyunderstood by a worker skilled in the art.

In various embodiments, the component signals are Zadoff-Chu sequenceswhich are transmitted in time rather than in frequency. That is, the PSSin existing LTE implementations is conveyed via a set of symbols whichare transmitted simultaneously and via a contiguous set of resourceblocks/subcarriers. In contrast, in embodiments of the presentinvention, each component signal may comprise the same elements as thePSS, but these elements may be conveyed via a set of symbols which aretransmitted via a set of resource blocks occurring sequentially in timeand associated with a common set of subcarriers. The set of symbols maybe contiguous.

Having reference to FIG. 2, embodiments of the present invention providefor a system for facilitating synchronization in a Long Term Evolution(LTE) cell. The system includes an evolved NodeB (eNB) 110 and at leastone User Equipment (UE) 130. The eNB 110 is configured to wirelesslytransmit a burst 120 of multiple component signals, each of thecomponent signals indicative of a Primary Synchronization Signal (PSS).Further, the burst is transmitted within a predetermined time frame, forexample within one or two subframes. The UE 130 is configured to receiveat least one and typically multiple component signals of the burst ofmultiple signals. The UE 130 is further configured to decode the PSSbased on the received at least one component signal. The UE 130 mayfurther be configured to perform 135 synchronization to the LTE cellbased at least in part on the decoded PSS. Additionally or alternativelyto performing synchronization, the UE may be configured to acquire 150symbol timing of the LTE cell based at least in part on the decoded PSS.

Having reference to FIG. 3, embodiments of the present invention providefor a method for facilitating synchronization of a User Equipment (UE)to a Long Term Evolution (LTE) cell serviced by an evolved NodeB (eNB).The method includes wirelessly transmitting 210, by the eNB, a burst ofmultiple component signals. Each component signal is indicative of aPrimary Synchronization Signal (PSS) and the burst is transmitted withina predetermined time frame. The method further includes receiving 220,by the UE, at least one signal of the burst of multiple signals. Themethod may further include decoding 230, by the UE, the PSS based on thereceived at least one signal. The method may further include initiating240, by the UE, synchronization to the LTE cell based at least in parton the decoded PSS. Additionally or alternatively to initiatingsynchronization, the method may further comprise acquiring 250 symboltiming of the LTE cell based at least in part on the decoded PSS.

FIG. 4 illustrates an LTE resource grid provided in accordance withembodiments of the present invention. An LTE resource grid isillustrated in which the PSS 310 is transmitted via a set ofsimultaneously transmitted symbols and via six contiguous resourceblocks in a given frequency band 315. Similarly, the SSS 320 istransmitted via another set of simultaneously transmitted symbols in thesame given frequency band 315 prior to transmission of the PSS. In thefollowing two subframes 330, 340, the ePSS 350 is transmitted (via thesame given frequency band 315 in the present example). As such, the ePSSmay be transmitted using the center six resource blocks of twosubframes, such as the two subframes following the subframe in which thePSS and SSS are transmitted. The ePSS may include multiple copies of thecomponent signal, each component signal being conveyed by a number ofcontiguous slots of a given resource block.

It is considered that, when the component signals are transmitted intime rather than in frequency, the same Zadoff-Chu sequence (same root)can be used as both the PSS and the component signals of the ePSS.Legacy UEs are configured to detect the PSS transmitted in frequency,and therefore would not typically interpret the component signals as aZadoff-Chu sequence. As such, false detection issues are mitigated.

In various embodiments, the component signals are substantiallyidentical to each other, for example each component signal correspondingto a particular Zadoff-Chu or other Constant Amplitude ZeroAutocorrelation (CAZAC) sequence which assists in identifying the cellserviced by the eNB transmitting the ePSS. The component signals may beidentical to the existing PSS, which may also be transmitted forbackward compatibility.

It is noted that, in various embodiments of the present invention,synchronization generally corresponds to downlink synchronization,rather than uplink synchronization.

As noted above, the ePSS may comprise a burst of component signals, eachcorresponding to a copy of a PSS. As such, the time required by a UE inlow Signal to Noise Ratio (SNR) conditions to receive a sufficientnumber of copies of the PSS for decoding may be reduced. Further, the UEmay not need to remain in a signal-receptive state for a long period oftime to receive this sufficient number of copies, and hence energyconsumption may also be reduced. For example, several component signalsmay be sent per subframe. Further, several contiguous or closely-spacedsubframes may be used to transmit component signals. In some exampleembodiments, each of multiple subframes may be used to convey up to 12component signals each.

In various embodiments, the component signals of the ePSS are Zadoff-Chutype signals, similarly to the currently standard PSS. However, whereasthe currently standard PSS utilizes only three of the possible roots ofa length-63 Zadoff-Chu sequence, the component signals may utilize rootsother than the three roots currently in use. Roots currently in use areroots 25, 29 and 34. It is considered herein that the length-63Zadoff-Chu sequence may have at least 36 possible roots including theseroots. Each eNB in a given region may use a different root. Further, twodifferent eNBs may be inhibited from using the same root unless they aresufficiently far from one another. This may allow for a UE to morereliably identify an eNB.

As noted above, the ePSS is configured to include multiple copies of theexisting PSS. This is considered herein to be a convenient choice sinceLTE eNBs are already configured to generate the PSS and LTE UEs arealready configured for detecting the PSS. As such, accommodating thetechnology disclosed herein may require only limited changes to currentLTE systems.

In various embodiments, a UE may be configured to decode the PSS byaccumulating plural copies thereof, for example corresponding to pluralcomponent signals of the ePSS. The UE may use a differentialautocorrelation or similar process to decode the PSS based on the pluralcopies. Decoding based on plural copies may facilitate coverage inmarginal signal conditions, since signal strength may be improved by aform of repetition coding.

In various embodiments, the ePSS includes several copies of theZadoff-Chu sequences indicative of the PSS, i.e. component signals,thereby facilitating reliable detection of the underlying PSS atrelatively low SNRs. In some embodiments, the ePSS includes greater than10 component signals. In some embodiments, the ePSS includes about 20component signals. In some embodiments, the ePSS includes about 40component signals.

In accordance with an aspect of the present invention, there is provideda method for facilitating synchronization of a User Equipment (UE) to aLong Term Evolution (LTE) cell serviced by an evolved NodeB (eNB). Themethod includes wirelessly transmitting, by the eNB, an ePSScorresponding to a burst of multiple component signals. Each componentsignal is indicative of a Primary Synchronization Signal (PSS). Theburst of multiple signals is transmitted within a predetermined timeframe. The method may further include receiving, by the UE, at least onesignal of the burst of multiple signals. The method may further includedecoding, by the UE, the PSS based on the received at least one signal.The method may further include performing, by the UE, further actionsrelated to synchronization to the LTE cell based at least in part on thedecoded PSS.

In accordance with another aspect of the present invention, there isprovided a system for facilitating synchronization in a Long TermEvolution (LTE) cell. The system includes an evolved NodeB (eNB) and atleast one UE. The eNB is configured to wirelessly transmit a burst ofmultiple signals. Each of the multiple signals is indicative of aPrimary Synchronization Signal (PSS). The burst of multiple signals istransmitted within a predetermined time frame. The UE is configured toreceive at least one signal of the burst of multiple signals. The UE isfurther configured to decode the PSS based on the received at least onesignal. The UE may further be configured to perform further actionsrelated to synchronization to the LTE cell based at least in part on thedecoded PSS.

In some embodiments, the UE may be configured to perform symbol timingacquisition based on the received at least one signal. The symbol timingacquisition may correspond to reacquisition or recovery of symbol timingfollowing a loss of timing synchronization, for example. The symboltiming acquisition may be performed as part of, in addition to, oralternatively to, the synchronization to the LTE cell.

In embodiments of the present invention, symbol timing acquisition andsynchronization to a cell are both examples of adjusting operation ofthe UE based on the ePSS.

FIG. 5 illustrates simulation results showing the probability ofdetection and false detection of a PSS as derived from plural componentsignals of an ePSS communicated in accordance with various embodimentsof the present invention. Various scenarios corresponding to the ePSSincluding 4, 10, 20 and 40 component signals (“reps”) are illustrated.Scenarios under which frequency division is or is not employed are alsoillustrated. The Detection Probability corresponds to the probabilitythat the PSS is successfully detected and decoded by the UE based on themultiple component signals. The False Alarm Rate corresponds to theprobability that a PSS is erroneously detected, for example due toincorrect detection of a PSS due to errors. For example, a falsedetection may occur because of errors that make a PSS look like a matchfor the expected signal. The SNR value in the simulation is about −14.2dB. The simulation results indicate that an ePSS including about 20component signals may be sufficient for providing about a 95% PSSdetection rate, with adequately low false alarm rate.

In various embodiments, the locations in time and frequency of the ePSSand/or its component signals may need to be known a priori by the UEs,particularly when the ePSS is not scheduled via the PDCCH. However, thelocation is not necessarily required to be in the center six PRBs. Insome embodiments, the ePSS location, such as a specification of the PRBsused to carry the ePSS, may be defined as part of the LTE specification.In other embodiments, to facilitate further resource optimization, theePSS location may be variable and communicated via an appropriate SystemInformation Block (SIB) transmitted periodically by the eNB. In yetother embodiments, the ePSS location may be transmitted to UEs viahigher layer signalling such as Radio Resource Control (RRC) orNon-Access Stratum (NAS) signalling layers.

It is noted that, in current LTE implementations, a PSS signal (andhence also a component signal of the ePSS) requires about 63 ResourceElements (RE), whereas one Physical Resource Block (PRB) in the PhysicalDownlink Shared Channel (PDSCH) has about 132 REs, although this mayvary depending on the current size of the Physical Downlink ControlChannel (PDCCH). As such, about two copies of a component signal of theePSS can be conveyed via the 132 REs of a PRB in the Physical DownlinkShared Channel (PDSCH).

However, in some embodiments it is considered that a repetition in timeof the component signals of the ePSS may trigger a false detection, asillustrated in FIG. 6. More specifically, if a UE is correlating on astrong signal in a window covering more than one PSS copy it will see afairly strong correlation at positions offset either side of the correcttime alignment. For example, if there are two copies that are the same,one after another, there will be at least a 50% match for positionsoffset one PSS either side of the 100%. In noisy conditions where thereare errors, the best match may therefore be at any of three possibletiming positions. In various embodiments, to mitigate the chance of afalse detection, repetitions in time may be avoided by adequate fillingof the resource blocks used to convey the ePSS. Additionally oralternatively, the ePSS may comprise different component signals indifferent subframes, each of the different component signalscorresponding to a different root M of the Zadoff-Chu sequence forexample as specified in Equation (1). This may provide for a strongcorrelation at the appropriate time.

In some embodiments, the example presented with respect to FIG. 6 mayhave a ramp up and down of possibly good match probabilities from thevarious levels of overlap with the sample window.

An example configuration is illustrated in FIG. 7, in which the ePSS 610is conveyed via two adjacent subframes 620, 630, such that the componentsignals 625 of the ePSS falling within the first subframe 620 correspondto a first root X of the Zadoff-Chu sequence and the component signals635 of the ePSS falling within the second subframe 630 correspond to asecond, different root Y of the Zadoff-Chu sequence. In variousembodiments, correct alignment of a window across the two subframes, 1and 2, is expected to correspond to the only time that generates a goodcorrelation. In this example the PSS copy roots are duplicated infrequency across two slots. In contrast, in the example corresponding toFIG. 6, the PSS copy roots are duplicated in time in the same two slotsand the two subframes. As illustrated in FIG. 7, the component signals625 include two identical copies of the PSS copy root X, each in 6 ofthe 12 frequencies available in a Resource Block.

In some embodiments, rather than transmitting two copies of a componentsignal within a resource block, the component signal may correspond to aroot of a longer CAZAC sequence, for example a Zadoff-Chu sequence oflength 132, given by:ZC ¹³² _(M)(n)=exp[−jπMn(n+1)/132],n=0,1, . . . ,132  (2)

A longer sequence may be configured such that it spans substantially allsymbols across a subframe, while using one subcarrier, for example.

Energy Consumption Considerations

Some embodiments of the present invention are configured to address anissue of potentially excessive energy used by UEs in DRX mode to decodethe PSS when the UEs are experiencing relatively low SNR conditions. Forexample, it is noted that, in current LTE implementations, before the UEcan decode the PDCCH, the UE typically needs to acquire appropriatetiming synchronization with the eNB. Acquisition may include: Carrierfrequency offset (CFO) estimation; Symbol timing estimation; Sub-frametiming estimation; Cell-ID verification; and Frame timing estimation.

In current LTE implementations, CFO and symbol timing acquisitionalgorithms typically rely on the cyclic prefix. Even in poorSignal-to-Interference-Plus Noise Ratio (SINR) conditions suchalgorithms are considered to perform well and use relatively littlepower. In addition, frame timing is typically not needed as long as theUE's crystal clock (XTAL) tolerance (PPM) doesn't drift by more than+/−5 ms each DRX sleep cycle. Sub-frame timing and cell ID verificationmay be accomplished by the detection of the PSS and SSS (correlationwith the previously obtained PSS and SSS). In some scenarios, PSSdetection at low SNRs of −14.2 dB can take up to about 300 ms for 90%detection probability and about 100 ms for 50% detection probability.FIG. 8 illustrates simulation results showing the probability ofdetection and false detection of a PSS as derived from plural copies ofthe PSS, whether received over time or within a burst corresponding tothe ePSS. Various scenarios corresponding to the number of copies of thePSS being 10, 24, 48, 72 and 96 are illustrated. The time inmilliseconds corresponds to the time taken for accumulating this numberof copies in existing LTE implementations without use of the burst ePSS.The Detection Probability corresponds to the probability that the PSS issuccessfully detected and decoded by the UE based on the multiple copiesof the PSS. The False Alarm Rate corresponds to the probability that aPSS is erroneously detected, for example due to detection of a PSS of aneighbouring cell. In various scenarios, PSS detection may equate totaking 90% to 67% of the power used by the UE when in idle DRX. In someembodiments, the possibility of false PSS detection can be mitigated byalso receiving the SSS. It is considered that performance of combinedPSS and SSS detection may potentially be quicker since this is a longersequence. For example, as described elsewhere herein, more than 3 and upto 36 roots of Equation (1) may be utilized in the ePSS to avoid falsedetection from adjacent cells. This can make it unnecessary to receivethe SSS if the ePSS can be relied upon to indicate that a UE is stillcamped on the same cell.

In various embodiments of the present invention, the number of PSScopies required by the UE for a successful decode may be substantiallythe same whether a legacy method of broadcasting PSS is used or whetherthe ePSS approach as described herein is used. However, when the ePSS issent in a relatively dense burst in the PSDCH, the time required tocommunicate this number of PSS copies, and hence the acquisition time,can be decreased. For example, in some embodiments, using the ePSSmethod, 24 copies of the PSS can be sent in 2 subframes. This assumes 6PRB, the maximum for the low complexity Rel. 13 UE. In contrast, alegacy method of broadcasting PSS may require 100 SF to transmit 20copies of the PSS.

As noted above, since the time required for a UE to successfully acquireand decode a PSS is reduced, total energy required for the task may alsobe reduced. However, the power saving in the above example may notsimply be a ratio of 2/100, since there are still several other stepsthat need to be performed and overhead to account for. A spreadsheetpower model was created in support of the present invention for analysisof the decode energy considerations. This model showed that the ePSStechnique can extend battery life by between 9 times and 3 times,relative to legacy methods and at low SNR (−14.2 dB). This range mayvary depending on various factors, such as legacy paging opportunitydecode time at low SNRs (5 ms-20 ms) and overheads such as warm-up time(e.g. turn radio on, code from Flash to RAM, Carrier Frequency Offset(CFO) estimation time, and Symbol timing estimation). The lower theoverhead becomes the larger the improvement may become (as apercentage). It is also considered that energy savings associated withthe present invention may be less for UEs which are in a relatively goodcoverage.

In various embodiments, the ePSS may be transmitted in less than allPaging Occasions (PO) and/or subframes (SF). It is considered thattransmitting the ePSS at every PO may consume a large amount of networkresources. To reduce resource consumption, PO locations may be assignedfor UEs which are at low SNR close after the ePSS is sent. Since the UEsat low SNR typically constitute a subset of all UEs in a cell, it isconsidered that, in various embodiments, the ePSS doesn't need to besent in every 10 ms Frame. Rather, in one embodiment, the ePSS may betransmitted every k Frames, where k=1/p and p is the proportion of UEsexperiencing a “low” SNR, that is an SNR below a threshold value. Thus,assuming 10% of UE are at low SNR, the ePSS only need to be sent every100 ms.

It is further contemplated that, in various embodiments, legacy UEs maypotentially be paged the majority of the time via the PDCCH, and UEs inCoverage Enhancement (CE) mode may be paged using a coverage enhancedform of ePDCCH. As such, the PDCCH capacity may remain balanced. FIG. 9illustrates such a configuration, including Coverage Enhancement PagingOpportunities 820 occurring up to about 10 ms after the ePSS 810, andlegacy Paging Opportunities 830 occurring at other times spread outbetween instances of the ePSS.

The proportion of network resources used by embodiments of the presentinvention to support the ePSS is given below for various examplescenarios. The ePSS in these examples corresponds to about 12 PRBs(about 24 repeats) every 100 ms.

-   -   For a 1.4 MHz system bandwidth (for example used in association        with Low-Cost or Limited-Capability UEs), the network resource        usage is about 12/(6*100)=2%.    -   For a 5 MHz system bandwidth, the network resource usage is        about 12/(25*100)=0.5%.    -   For a 10 MHz system bandwidth, the network resource usage is        about 12/(50*100)=0.24%    -   For a 20 MHz system bandwidth, the network resource usage is        about 12/(100*100)=0.12%.

In some embodiments, at a relatively small increase in UE powerconsumption, a single ePSS may be used to synchronize UEs with POs thatspan longer than 10 ms. In some such embodiments, after the UE detectsthe ePSS it may be required to stay awake or go to sleep with arelatively high accuracy crystal-driven clock until its PO occurs.Sleeping may save more power, however the crystal accuracy needs to bebetter than ½ of a symbol to avoid loss of SF timing during sleep. Forexample a crystal accuracy of at least (½)*( 1/14)ms=36 microseconds maybe required. A relatively inexpensive, well-trained XTAL may have anaccuracy of about 10 PPM which allows a sleep time of 3.6 seconds beforesymbol timing is lost. For such a crystal clock accuracy, the ePSS maybe transmitted periodically with a period of up to 3.6 seconds.

In some embodiments, as mentioned above, the UE may be configured toperform symbol timing acquisition, such as first-time acquisition orsymbol timing reacquisition or recovery, based on the received signal.Symbol timing recovery may be performed when the UE loses accuratesymbol timing synchronization with the wireless communication system,for example upon waking up from an extended period of sleep, in responseto a clock drift condition which indicates symbol timing has potentiallybeen lost.

Conventionally, in OFDM based systems, the UEs reacquire the timingusing cyclic prefix (CP) autocorrelation and/or by detecting thesynchronization reference signals which are transmitted periodically bythe base-station. The reacquisition time is inversely proportional tothe Signal-to-Noise Ratio (SNR), which may be significant in marginalsignal conditions. This is a particular problem in the new LTE EnhancedCoverage operation. Long reacquisition times may cause higher UE powerconsumption and delay upon wake-up.

In various embodiments, the UE is configured to acquire timing based atleast partially on the ePSS. For example, a plurality of copies of thePSS as included in a burst corresponding to the ePSS may be decoded todetermine the system's symbol timing.

In some embodiments, the UE can obtain the 5 ms sub-frame timing bydetecting the PSS, but it will not know whether it is in the first halfof the radio frame (corresponding to the detection of the PSS atsub-frame 0) or the second half (corresponding to the detection of thePSS at sub-frame 5). This ambiguity can be resolved by detecting the SSSwhich is transmitted one symbol before the PSS. The SSS on sub-frame 0is different from the one on sub-frame 5, and the UE can exactlydetermine the subframe number depending on the SSS pattern it detects.

Frame Timing and DRX Considerations

Some embodiments of the present invention are configured to address anissue related to UE clock drift, UE synchronization loss and/or frametiming when a long DRX time interval is used by a UE. For example, whena UE's DRX interval is sufficiently long, the UE's internal crystalclock (XTAL) timing accuracy may degrade to the point that a clocksynchronization error range exceeding+/−5 ms is possible. For a 10 ppmXTAL, this occurs after 8.3 minutes of sleep. If such a timing accuracycondition occurs, it may be desirable to re-acquire the PhysicalBroadcast Channel (PBCH). Re-acquiring the PBCH at low SINRs isconsidered to take a relatively long time, for example the time requiredfor 99^(th) percentile detection may exceed 1000 ms, as set forth in the3GPP document numbered R1-144601 and entitled “3GPP TSG RAN WG1 Meeting#79, Coverage Enhancement PBCH Simulation Results and Proposals,” SierraWireless, San Francisco, USA, 17-21 Nov. 2014. Such a re-acquisition ofthe PBCH may also consume significant battery energy.

As noted above, in various embodiments of the present invention, theePSS is sent less frequently than every 10 ms, for example every 100 ms,and further the ePSS is sent at a System Frame Number (SFN) which may beknown a priori to a UE. As such, it is considered that the timing driftdue to an inexpensive crystal clock of the UE may be greater than, e.g.100 ms (rather than 10 ms) before frame synchronization is lost. As anexample, for a UE employing a crystal clock having an accuracy of about10 PPM, sleep time may up to about 83 minutes before a loss of Frametiming occurs. As such, a relatively long potential sleep time may beprovided for in some embodiments, when compared to prior artcapabilities.

SSS Detection Considerations

Some embodiments of the present invention are configured to address anissue related to the need for a UE to detect the SecondarySynchronization Signal (SSS), for example following detection of thePSS. As will be readily understood by a worker skilled in the art,detection of the SSS is typically required for full identification ofthe cell-ID. Further, decoding of the SSS typically requires informationobtained from decoding of the PSS. It is also considered that the PSS onits own may potentially not provide sufficient information on its own toreliably confirm SF timing or Cell ID. This is due to a non-negligibleprobability that a UE will mistakenly decode a neighbouring eNB's PSSrather than the PSS of the eNB of the cell on which it is camped.Because only three PSS signal are used, one for each sector, a UE maypotentially receive the PSS of a neighbouring eNB. This is particularlya concern for UEs in Coverage Enhancement (CE) mode. Further, it isconsidered that the SSS detection performance may be undesirably low duefor example to the poor auto-correlation properties of the SSS.

Various embodiments of the present invention may be configured tofacilitate synchronization of a UE with a desired eNB by assigningdifferent eNBs to use different ones of the unused Roots (i.e. rootsother than Roots 25, 29, 34 that are co-prime with the sequence length)of Equation (1) for its PSS, and such that a predetermined amount ofspacing between eNBs using the same root is used. This is in contrast tocurrent LTE implementations which utilize only three roots. Each eNB maybe configured to use, for the ePSS thereof, one or more selected rootsof Equation (1) such that these selected roots are not re-used byanother eNB within a predetermined distance. That is, the spatial re-usepattern of roots may be configured to avoid nearby eNBs utilizing thesame roots. As such, a UE may verify that it is still decoding the samecell when the observed root as derived from the ePSS is unchanged. Assuch, the UE may not be required to decode the SSS in order to verifywhich cell is being decoded.

In some embodiments, when all viable roots of Equation (1) are in use,and/or when all combinations of patterns of these roots are in use,there is expected to be relatively little chance the UE wouldaccidentally decode a neighbour ePSS. In some embodiments, a root re-usepattern of seven is utilized as illustrated in FIG. 10. For example,cells with same labels c_(i) (1=1, 2, . . . 7) may utilize the sameroots for ePSS transmission, while cells with different labels mayutilize different roots.

In some embodiments, less than all but more than three of the roots ofEquation (1) may be used, thereby providing more than three PSS signalsfor identifying cells and reducing the need to rely on the SSS for cellidentification. For example, in one embodiment, seven different roots ofEquation (1) are used to provide seven different PSS signals rather thanthree as used currently.

In some embodiments, rather than using roots other than the three rootsof Equation (1) already in use, i.e. roots 25, 29 and 34, the ePSS maybe formed from patterns of these three roots. As such, UEreconfiguration may be reduced, since sequences corresponding toadditional roots need not be stored in UE memory. For example, the ePSSmay comprise unmatched pairs of the three roots mentioned above, suchthat a first pair of the roots is transmitted in a first subframe onadjacent frequencies, and a second pair of the roots is transmitted inthe following subframe. It is contemplated that there may be 18different combinations of roots in such a configuration that do notrepeat the same root on the same frequency. Avoidance of repeated rootsmay be desired since, if a root is repeated, there may be a 50% chanceof the UE making a correlation match for that frequency for one subframeoffset either side of the correct timing, which may result in a falsedetection of the time. In some embodiments, the above configuration with18 combinations of roots may allow a reuse pattern that may likely avoidthe UE incorrectly detecting an ePSS from a neighbouring eNB. In variousembodiments, the pattern of roots may be known a priori to the UE, forexample via communication of the pattern to the UE using a broadcastedSIB or higher-layer signalling means. FIG. 11 illustrates an example ofthis configuration, in which a first subframe includes two componentsignals 1010, 1020 of the ePSS corresponding to two roots of Equation(1), namely roots 25 and 29, respectively, and in which a second,subsequent subframe includes two component signals 1030, 1040 of theePSS corresponding to two roots of Equation (1), namely roots 29 and 34,respectively. The four component signals 1010, 1020, 1030, 1040 may betransmitted in time, one after another.

In some embodiments, as the number of Resource Blocks (RBs) and/or thenumber of roots used for conveying the ePSS increases, the number ofdifferent potential combinations of roots used in the ePSS maycorrespondingly increase. In some embodiments, different frequencies maybe used in different cells to convey the ePSS. In some embodiments,different blocks of RBs may be used in different cells to convey theePSS.

FIG. 12 illustrates ePSS and PO timing with a 3.6 second interval, inaccordance with an embodiment of the present invention. In someembodiments, a single ePSS may be used to synchronize UEs with POs thatoccur greater than 10 ms from the ePSS. To maintain power efficiency,after the UE detects the ePSS, it would go back into the deep sleep modeand then wake-up again just before its PO. For this to work, while theUE is in deep sleep, the clock accuracy needs to make sure the UEdoesn't lose SF timing. For example, in one embodiment, the UE couldonly stay in deep sleep after the ePSS for a maximum of 3.6 seconds,assuming a XTAL accuracy of ±10 PPM. Thus, the ePSS could be sent with amaximum period of 3.6 sec assuming a XTAL accuracy of ±10 PPM. It isobserved that, in some embodiments, the ePSS may be sent infrequentlywith a period up to 3.6 seconds assuming an XTAL accuracy of +/−10 PPM.

ePSS with Paging Indicator (PI)

Some embodiments of the present invention relate to an ePSS with PagingIndicator, as follows. Since decoding the PO may use a fair bit of thepower (for example 45%), this could be reduced if the ePSS is used bothfor SF synchronization and to indicate if a page is going to be sent inits upcoming PO or not. To indicate this, different PSS rootsets/combinations can be sent; one root set to indicate when there is apaging coming in the upcoming PO and a different root set to indicate ifthere is no page coming and thus the UE can go directly to sleep afterePSS decoding without needing to stay awake to try and decode the PO.The amount of power saving will depend on how often a page is being sentin the PO for that UE. As shown in the annex, the ePSS detectionperformance only degrades slightly when the UE needs to search for twopossible root sets so detection time is still about 4 SF times 6 PRBsfor 90-95% detection probability at SNR corresponding to 15 dB gain.

FIG. 13 illustrates ePSS with paging indicator, in accordance with anembodiment of the present invention.

It is observed that, in some embodiments, an ePSS may additionallycommunicate if a page is going to be sent in the upcoming PO or not.

In some embodiments, assuming that 10% of the time a page is sent at thePO (i.e. so 90% of the time the UE can go directly to sleep afterdecoding the ePSS), for the “Receive only” use case with the DRXcycle=30 sec, the power consumption usage breaks down as in the TABLE 1.

TABLE 1 Baseline ePSS with Paging Ind. % % mWH Power mWH Power per DayUsed per Day Used Wake from Deep Sleep 0.4 2.5% 0.4 13.9% PSS/SSSAcquisition 13.8 86.3% 1.6 55.5% MIB Acquisition 0.0 0.0% 0.0 0.0% DRXDecode PO 1.4 8.5% 0.4 15.3% Deep Sleep 0.4 2.8% 0.4 15.4% Battery Life(Months) 10.4 57.8 % improvement NA 556%

It is observed that, in some embodiments, when the ePSS additionallycommunicates the paging status, the ePSS may reduce battery consumptionby >5 times.

Providing Accurate Time Information to UEs

In accordance with some embodiments of the present invention, there isprovided a method and system for facilitating provision of accurate timeinformation to UEs that rely on aggregation of multiple receptions ofdata to adequately receive downlink data. Such UEs may be operating in aCoverage Enhancement mode, for example.

For example, UEs in an LTE system that require aggregation of multiplereceptions in order to clearly receive the eNB downlink may not be ableto receive the accurate time information contained in System InformationBlock 16 (SIB16), since the time information changes frequently as timeprogresses. It is further noted that SIB16 information, like accessclass barring information, is typically not flagged as having changed inlegacy LTE systems, since frequent change is expected.

In some embodiments of the present invention, an SIB may be used toconvey accurate time stamp information to UEs. In some embodiments, theSIB may be a new SIB used for servicing UEs such as low-cost, limitedcapability and/or coverage-enhanced UEs, such as an SIB of this typeproposed for Release 13 of the 3GPP LTE specification. A reference tothe proposed SIB is as follows: “LS on simultaneous receptionrequirements and SIBs for MTC UEs,” 3GPP TSG RAN WG1 Meeting #79R1-145416 San Francisco, USA, 17-21 Nov. 2014.

In some embodiments, the new SIB may be configured to include a set ofaccurate time stamp information, which may be repeated within multiplesuccessive copies of the new SIB. At a time after the information shouldhave been received, another downlink transmission event may be providedand configured to mark the time at which the accurate information shouldbe applied. The marker event may be configured to have highintelligibility for reception in a weak signal environment. The markerevent does not necessarily need to convey other information, but rathermay be a substantially stand-alone signal. UEs may be configured toemploy correlation of the pattern of a known marker transmission toenhance reception success. The time information conveyed by the SIB andtriggered by the marker event may be assumed by the UE to be applicableat a known point such as a point in time corresponding to a peakcorrelation of the received signal with the known marker, as used by theUE to detect the marker event.

In some embodiments, the time mark may be considered to be at apredetermined point in time relative to the marker transmission, such asthe beginning, end or at some time during, before or after the markertransmission. In some embodiments, it may be desirable and practical toapply the time marker at a predetermined amount of time after the markertransmission to allow for decoding and verification rather thanretroactively applying the time marker to a time earlier that theconfirmed reception of the marker.

In various embodiments of the present invention, the ePSS describedabove may also function as the time marking event. The ePSS may be aviable candidate for this function since it is considered to potentiallyhave characteristics which would make it useful for this purpose. Invarious embodiments, the timing of the ePSS may be configured incoordination with requirements for providing of the time information inthe new SIB.

In various embodiments, low-cost or limited-capability (LC) UEs maycorrespond to low complexity User Equipment such as those proposed forstandardization by the 3rd Generation Partnership Project (3GPP). Thiscategory is primarily intended for use in Machine TerminatedCommunication (MTC) applications in LTE networks. Release 12 of the LTEstandard is planned to explicitly accommodate Category 0 UEs that arelimited in their capabilities relative to other categories. Release 13will define another category of LC UEs that will have certainlimitations relative to Category 0 UEs, such as communication bandwidthand/or computation limitations.

In various embodiments, simulations such as those identified herein toillustrate aspects of the present invention follow simulation settingsas set out in TABLE 2.

TABLE 2 Parameter Setting DL Bandwidth 1.4 MHz Sampling Rate 1.92 MHzSNR for 15 dB coverage −14.2 dB Antenna Configuration 2 × 1 ChannelModel EPA Max. Doppler Shift 1 Hz MIMO Correlation Low Carrier FrequencyOffset (CFO) 1 kHzResynchronization of UE and Base Station

In accordance with embodiments of the present invention, there isprovided a method and apparatus for using enhanced PSS (ePSS)transmitted from a base station for example, an eNB, for use by UEs forresynchronization of the UE with the base station. For thisresynchronization, it is assumed that the UE has knowledge of the PSSand SSS, which can be indicative of the feature that the base stationservicing the UE has not changed, however the carrier frequency offset(CFO) and timing are unknown to the UE.

According to embodiments, using ePSS, for example a dense burst of oneor more of PSS, SSS and other synchronization signals, forresynchronization can improve resynchronization of the UE with the basestation. However, the amount of network resources, for example time andfrequency, for an ePSS to provide a suitable single shot detection, forexample 90th percentile detection, can be high. For example, withreference to FIG. 14, simulations indicate that, at 155 dB MCL, the ePSSneeds to be 24 physical resource blocks (PRBs) to provide 90thpercentile detection with a false alarm of 0.1%. For example 4SF*6PRB=24 PRBs.

Furthermore, for 164 dB, which is 9 dB above the simulation results,assuming linear gain, the ePSS resources required to obtain 90^(th)percentile detection would be 10{circumflex over ( )}( 9/10)*24=190PRBs. It is apparent that this level of resources required can beprohibitively large, while 10% of the time, the UE would fail toresynchronize using the single ePSS. In addition, if the ePSS is sentinfrequently, for example every one second, the UE would need to wait 1sec before the next copy of the ePSS is sent, which may be prohibitivelylong. FIG. 15 illustrates the placement of ePSS in relation to legacyPSS/SSS for resynchronization of a UE with a base station, in accordancewith embodiments of the present invention.

According to some embodiments, if the UE fails to resynchronize using afirst instance of the ePSS, the UE can use the legacy PSS/SSS signals,however this may take approximately 2.5 seconds.

According to some embodiments, when resynchronization of the UE and thebase station using the ePSS fails to decode on the first attempt, the UEcan non-coherently or coherently combine the failed ePSS results withthe legacy PSS/SSS results in order to resynchronize the UE with thebase station, for example the eNB.

According to embodiments, failure to decode the ePSS can be consideredto occur when a correlation threshold is not met. For example, thecorrelation threshold can be a value necessary to achieve apredetermined rate of false detection. For example, the correlationthreshold can be indicative of a less than 0.1% rate of false detection.It is understood that ePSS correlation results can specifically refer toan array of correlation results.

According to embodiments, the improvement in resynchronization timebased on the correlation between ePSS and PSS/SSS can be approximated tobe 10 ms*ePSS_size, wherein ePSS_size is in units ofLegacy_Resync_Size=(2 PSS symbols+2 SSS symbols)*6 PRBs=4symbols×6PRBs=24 symbols×PRBs.

As an example, if the size of the ePSS is 12 Symbols×96 PRBs then theePSS_Size is (12*96)/(24)=48 units of Legacy_Resync_Size. Accordingly,when ePSS is combined with PSS/SSS, the resynchronization time can beimproved by approximately 48*10 ms=480 ms.

According to embodiments, the ePSS can provide more than just symboltiming but can also provide subframe (SF) timing, and the ePSS can besent with different timing within the SF (for example the ePSS can endat the end of the SF). As such, the PSS/SSS (which can be sent in symbol5 and 6 of the SF as shown in FIG. 4) is not time aligned with the ePSS.As such, the results of the ePSS or PSS/SSS need to be time adjusted byshifting the sequence or by zero padding the reference correlationsequence before combining. For example, the reference correlationsequence for the first set of synchronization signals is zero paddedbefore combining.

According to embodiments, the method for resynchronizing a UE and a basestation, includes transmitting a first set of synchronization signalsand a second set of synchronization signals, wherein the time andfrequency of the first set of synchronization signals is know a priorito the UE. In addition, the time and frequency of the second set ofsynchronization signals is sent wirelessly to the UE, for example thesecond set of synchronization signals can be the ePSS. During initialsynchronization of the UE with the base station, the UE uses the firstset of synchronization signals to synchronize to the base station.

According to embodiments, at a subsequent time, in order toresynchronize the UE with the base station, the UE uses the second setof synchronization signals to synchronize to the base station. If atthis subsequent time the UE fails to synchronize with the base stationusing the second set of synchronization signals, the UE uses a modifiedset of synchronization signals to synchronize with the base station,wherein the modified set of synchronization signals is a combinedversion of the first set of synchronization signals and the second setof synchronization signals.

According to some embodiments, the second set of synchronization signalsare time adjusted before they are combined with the first set ofsynchronization signals. According to some embodiments, the first set ofsynchronization signals are time adjusted before they are combined withthe second set of synchronization signals.

According to some embodiments, the results of reception of the secondset of synchronization signals are time adjusted before they arecombined with the results of reception of the first set ofsynchronization signals. According to some embodiments, the results ofreception of the first set of synchronization signals are time adjustedbefore they are combined with the results of reception of the second setof synchronization signals.

According to some embodiments, the second set of synchronization signalsare non-coherently combined with the first set of synchronizationsignals, thereby creating the modified synchronization signals.According to some embodiments, the second set of synchronization signalsare coherently combined with the first set of synchronization signals,thereby creating the modified synchronization signals. According to someembodiments, the modified synchronization signals used to synchronizethe UE and the base station are generated by using a correlation of thesecond set of synchronization signals.

According to some embodiments, the results of reception of the secondset of synchronization signals are non-coherently combined with theresults of reception of the first set of synchronization signals,thereby creating the modified synchronization signals. According to someembodiments, the results of reception of the second set ofsynchronization signals are coherently combined with the results ofreception of the first set of synchronization signals, thereby creatingthe modified synchronization signals. According to some embodiments, themodified synchronization signals used to synchronize the UE and the basestation are generated by using a correlation of the results of receptionof second set of synchronization signals.

According to some embodiments, the first set of synchronization signalsare zero padded signals.

Methods and systems related to LTE wireless communication networksinvolving base stations such as eNBs and various types of UEs have beendescribed herein. Parts and operation of existing eNBs and UEs will bereadily understood by a worker skilled in the art. Further, it iscontemplated that existing eNBs and UEs may be modified to operate inaccordance with the present invention at least in part byreconfiguration of the operating instructions, routines and protocolsexecuted thereby. Such modification may involve modification of machineinstructions held in software or firmware of one or more electronicdevices, modification of logic hardware such as Field Programmable GateArrays (FPGAs), modification of signal processing hardware, or the like,or a combination thereof.

FIG. 16 illustrates an eNB and a UE provided in accordance with anembodiment of the present invention. The eNB 1300 includes at least amicroprocessor 1305, a memory 1310 containing program instructions forexecution by the microprocessor, a signal processing unit 1315 and aradio transceiver 1320. The UE 1350 similarly includes at least amicroprocessor 1355, a memory 1360 containing program instructions forexecution by the microprocessor, a signal processing unit 1365 and aradio transceiver 1370. The UE also includes a clock circuit 1375. Thecomponents of a signal processing unit may overlap with the componentsof corresponding radio transceiver. The signal processing unit and/ortransceiver may be configured in accordance with the present inventionthrough hardware, firmware, or both.

The microprocessor, signal processing unit and transceiver of the eNBare cooperatively configured to wirelessly transmit a burst of multiplesignals, each indicative of a Primary Synchronization Signal (PSS), theburst of multiple signals transmitted within a predetermined time frame.The microprocessor, signal processing unit and transceiver of the UE arecooperatively configured to receive at least one signal of the burst ofmultiple signals; decode the PSS based on the received at least onesignal; and adjust operation based at least in part on the decoded PSS.The microprocessor of the UE is further configured to perform thecombining functions as disclosed elsewhere herein. Adjusting operationmay include adjusting operation of the clock circuit 1375, for exampleby adjusting one or more of the clock time, the clock frequency and theclock phase.

It will be appreciated that, although specific embodiments of theinvention have been described herein for purposes of illustration,various modifications may be made without departing from the spirit andscope of the invention. In particular, it is within the scope of theinvention to provide a computer program product or program element, or aprogram storage or memory device such as a solid or fluid transmissionmedium, magnetic or optical wire, tape or disc, or the like, for storingsignals readable by a machine, for controlling the operation of acomputer according to the method of the invention and/or to structuresome or all of its components in accordance with the system of theinvention.

Acts associated with the method described herein can be implemented ascoded instructions in a computer program product. In other words, thecomputer program product is a computer-readable medium upon whichsoftware code is recorded to execute the method when the computerprogram product is loaded into memory and executed on the microprocessorof the wireless communication device.

Acts associated with the method described herein can be implemented ascoded instructions in plural computer program products. For example, afirst portion of the method may be performed using one computing device,and a second portion of the method may be performed using anothercomputing device, server, or the like. In this case, each computerprogram product is a computer-readable medium upon which software codeis recorded to execute appropriate portions of the method when acomputer program product is loaded into memory and executed on themicroprocessor of a computing device.

Further, each step of the method may be executed on any computingdevice, such as a personal computer, server, PDA, or the like andpursuant to one or more, or a part of one or more, program elements,modules or objects generated from any programming language, such as C++,Java, PL/1, or the like. In addition, each step, or a file or object orthe like implementing each said step, may be executed by special purposehardware or a circuit module designed for that purpose.

It is obvious that the foregoing embodiments of the invention areexamples and can be varied in many ways. Such present or futurevariations are not to be regarded as a departure from the spirit andscope of the invention, and all such modifications as would be obviousto one skilled in the art are intended to be included within the scopeof the following claims.

What is claimed is:
 1. A method for resynchronizing a User Equipment(UE) to a base station, the method comprising: receiving, by the UE, afirst set of synchronization signals; receiving, by the UE, a second setof synchronization signals; and resynchronizing, by the UE, with thebase station using the second set of synchronizing signals, wherein whenresynchronizing with the base station using the second set ofsynchronizing signals fails, the method further comprising: combining,by the UE, the first set of synchronizing signals and the second set ofsynchronizing signals to form a modified set of synchronizing signals;resynchronizing, by the UE, with the base station using the modified setof synchronizing signals.
 2. The method according to claim 1, whereinthe combining is non-coherent combining.
 3. The method according toclaim 1, wherein the combining is coherent combining.
 4. The methodaccording to claim 1, wherein the second set of synchronization signalsare time adjusted before combining the first set of synchronizingsignals and the second set of synchronizing signals.
 5. The methodaccording to claim 1, wherein the first set of synchronization signalsare time adjusted before combining the first set of synchronizingsignals and the second set of synchronizing signals.
 6. The methodaccording to claim 1, wherein the first set of synchronization signalsare zero padded before combining the first set of synchronizing signalsand the second set of synchronizing signals.
 7. A User Equipment (UE)for resynchronization with a base station, the UE comprising: aprocessor; and a machine readable memory storing machine readableinstructions which when executed by the processor configure the UE to:receive a first set of synchronization signals; receive a second set ofsynchronization signals; and resynchronize with the base station usingthe second set of synchronizing signals, wherein when theresynchronizing with the base station using the second set ofsynchronizing signals fails, the machine readable instructions furtherconfigure the UE to: combine the first set of synchronizing signals andthe second set of synchronizing signals to form a modified set ofsynchronizing signals; resynchronize with the base station using themodified set of synchronizing signals.
 8. The UE according to claim 7,wherein the machine readable instructions configure the UE tonon-coherently combine the first set of synchronizing signals and thesecond set of synchronizing signals to form the modified set ofsynchronizing signals.
 9. The UE according to claim 7, wherein themachine readable instructions configure the UE to coherently combine thefirst set of synchronizing signals and the second set of synchronizingsignals to form the modified set of synchronizing signals.
 10. The UEaccording to claim 7, wherein the machine readable instructionsconfigure the UE to time adjust the second set of synchronizationsignals before combining the first set of synchronizing signals and thesecond set of synchronizing signals.
 11. The UE according to claim 7,wherein the machine readable instructions configure the UE to timeadjust the first set of synchronization signals before combining thefirst set of synchronizing signals and the second set of synchronizingsignals.
 12. The UE according to claim 7, wherein the machine readableinstructions configure the UE to apply zero padding to the first set ofsynchronization signals before combining the first set of synchronizingsignals and the second set of synchronizing signals.
 13. A method forresynchronizing a User Equipment (UE) to a base station, the methodcomprising: receiving, by the UE, a first set of synchronizationsignals; receiving, by the UE, a second set of synchronization signals;and resynchronizing, by the UE, with the base station using the secondset of synchronizing signals; wherein the first set of synchronizationsignals are zero padded and combining the first set of synchronizingsignals that are zero padded and the second set of synchronizingsignals.
 14. The method according to claim 13, wherein the combining isnon-coherent combining.
 15. The method according to claim 13, whereinthe combining is coherent combining.
 16. A User Equipment (UE) forresynchronization with a base station, the UE comprising: a processor;and a machine readable memory storing machine executable instructionswhich when executed by the processor configure the user equipment to:receive a first set of synchronization signals; receive a second set ofsynchronization signals; and resynchronize with the base station usingthe second set of synchronizing signals; wherein the first set ofsynchronization signals are zero padded and combining the first set ofsynchronizing signals that are zero padded and the second set ofsynchronizing signals.
 17. The UE according to claim 16, wherein thecombining is non-coherent combining.
 18. The UE according to claim 16,wherein the combining is coherent combining.